The use of oblique illumination to investigate objects is advantageous for structured samples, since the surface structures results in diffraction effects that make the surface appear sculptural and contrasty. An oblique illumination is often used for investigating wafers or metal surfaces.
An “oblique illumination” is understood according to item 2.20.6 of DIN ISO 10934-1 as an “illumination having a ray bundle whose axis forms an angle with the optical axis of the microscope.” An oblique illumination is usually generated by introducing an aperture diaphragm into the illumination beam path and shifting it laterally outward away from the optical axis. A diaphragm arrangement of this kind for generating an oblique illumination in a microscope is presented, for example, in DE 35 27 426 C1, in which an iris diaphragm element is held on a threaded rod and can be shifted laterally by the rotation of a nut and of the threaded rod, so as thereby to modify the illumination angle. Actuation is cumbersome and time-consuming.
DE 10 2010 042 351 describes a microscope illumination system having a diaphragm device, which system generates an incident-light beam path proceeding decentrally with respect to the optical axis. The decentering is achieved by means of a rotatable diaphragm disk having different diaphragm openings. The diaphragm disk is located in the illumination aperture plane, and possesses multiple different diaphragm openings that correspond to the images of the various objective pupils.
Proceeding from this existing art, what is desired is a diaphragm arrangement with which, in particular, the illumination angle can be quickly and easily modified.